The present invention relates to high pressure concrete pumping apparatus and particularly to such pumping apparatus for transmitting of semi-fluid products such as concrete over relatively long distances.
Cement, concrete, plaster and similar building materials are advantageously transmitted through suitable flow lines from a central source, such as a mixing station or dump site to the deposit location. For example, in bridges, tall buildings and other structures, the transport of the material in batches was the normal method of carrying the materials for many years. However, concrete pumping apparatus has been developed which permits more or less continuous delivery of such material through a flow system constructed at the site. In many applications, relative long pumping lines are required for carrying the concrete from a central location to the deposit site. Further, the flow path may includes substantial vertical rising portions. For example, in the construction of cooling towers for nuclear power stations, the concrete has been historically raised through the use of buckets carried by suitable elevating means such as temporarily installed elevators, cranes and the like. In addition to being time consuming, such batch systems may create dangerous environments. Thus, if a concrete-filled bucket at the end of a crane inadvertently swings and strikes the structure, severe damage can result to both the property and the workmen. The pumping of concrete substantially eliminates such problems. Concrete pumping systems generally include positive displacement pumps to produce flow through the lines and various means have been suggested to create constant movement and delivery. Generally, multiple pumping arrangements have been suggested with alternate pump operation, and in some instances overlapping operation, provided in an attempt to develop essentially constant delivery of the pump material. Different systems use mechanical interlocks to effectively transfer the motion between the several pump units. Alternatively, various valving and interlocking flow mechanisms are used in the attempt to maintain the constant flow.
Generally, the prior art pump units involve some slight delay during the pumping cycles in which the pumping force decreases or drops sufficiently to permit effective stopping of the flow through the system. When the outward pumping action is again initiated, even though only a momentary delay is involved, substantial and significant inertia and friction forces within the system must be overcome.
The flow characteristics of the concrete or other similar semi-fluid material thus establish significant loads on the pumping system and may result in a complete failure of flow, with a resulting down time as well as relatively costly system clean-out required.
Another very significant factor which arises from the usual flow characteristic is the pulsating or recoil forces on the flow lines. The varying forces in flow cause movement of the flow line. Under certain conditions, the flow line movement is often sufficiently great as to create a hazardous condition. For example, with the flow line attached to a structure for carrying of concrete to the upper or top portion, the line movement may shake the building. For example, shaking of previously set concrete may result in a force which breaks the bond between the concrete and the reinforcing rods, with resulting weakening of the structure. With present systems, the elbows of the flow line system are embedded in relatively massive reaction blocks to minimize line movement. Such a system for example is disclosed in an article at page 379 of Concrete Construction magazine of June, 1979. As more fully described therein, a coupling elbows is advantageously embedded in a reaction block formed of more than one yard of concrete. Thus, an 8,000 lbs. concrete reaction block serves to firmly support and stabilize the flow line, minimizing the movement of the line and thereby shaking of the interconnected elements. In other applications, one or two men may be placed on the flow line to steady and support the line during the pumping operation. Even with two men, the pulsating effect may be so great as to create a force capable of knocking the men over. Further, the flow line must often be repositioned, at least at the upper end for most advantageous depositing of the concrete. It is therefore desirable to have a line system which can be crane mounted. Obviously with the highly pulsating effect associated with many conventional systems, crane mounting is difficult if not impossible unless very special crane constructions and supports are supplied.
In summary, the pulsating effect associated with the conventional prior art flow systems not only create problems within the pumping system but create very significant problems in connection with the associate components and personnel, all which have required rather special consideration and expense.
Further mechanical devices inherently are subject to wear, particularly in the environment of harsh materials such as concrete. Thus, even though the devices might operate satisfactorily when first constructed if sufficient attention has been given thereto, the components may rapidly lose the original characteristic. A lack of a significant operating life will of course prevent practical implementation of a design.
Thus, although the concrete pumping apparatus provides improved movement of concrete over the conventional bucket system and such apparatus is widely used in building and rod constructions, concrete pumping apparatus is not presently available which is particularly satisfacory for job application in which relatively long distances or significant vertical heights are encountered.